1. Field of the Invention
The present invention relates to a device for use in retrieving debris from a well and to a corresponding method. In particular, but not exclusively, the present invention relates to a device for use in retrieving debris from a well of a type which circulates fluid into an annulus defined between the device and a well borehole wall.
2. Background Art
In the oil and gas exploration and production industry, it is frequently necessary to carry out a procedure to retrieve debris from a well. For example, debris such as part of a tool or tool string or other “junk” can become stuck or lodged downhole and requires to be retrieved to surface in a “fishing” operation, such that a further well procedure may be carried out, or such that an existing procedure may be continued. Also, it is frequently necessary to clean a well by retrieving debris particles which have collected in a casing-lined borehole, before the well can be completed by installation of production tubing. Such debris particles may include cement lumps, rocks, congealed mud, oxidation lumps, metal debris, scale, slivers, shavings and burrs, for example.
U.S. Pat. No. 4,545,432 (Robert T. Appleton) discloses a wash-over type downhole retrieving device or fishing tool consisting of a hollow cylindrical body having an open lower end. The body has concentric inner and outer walls defining an annular space in which an annular piston can force down an annular sleeve of a malleable alloy having downwardly extending finger-like formations. The inside of the lower end of the outer wall is of cupped configuration effective to deflect the fingers inwards and over the open end of the body, so as to trap and retain an object for retrieval. The annular piston is forced down hydraulically by dropping a diverter ball valve and cutting teeth are optionally provided on the outer periphery of the lower end of the outer wall, on a detachable shoe. Tools of the type disclosed in U.S. Pat. No. 4,545,432 are not suited for the purpose of retrieving debris other than objects forming part of a downhole tool or tool string, and do not provide fluid circulation to the annulus during retrieval of objects.
Reverse circulating junk basket tools have also been developed which circulate fluid from the tool into the annulus, the fluid travelling along the annulus into a lower tool opening, and returning to the annulus at an upper location. These tools may include finger shoes for retrieving loose junk on the bottom of the hole, the fingers designed to close in beneath an object when slowly lowered during rotation. These tools suffer from disadvantages including that the flow rate of fluid to the annulus is insufficient to effectively retrieve loose debris, and that a large portion of the fluid directed into the annulus is lost uphole, rather than circulated downhole and into a lower opening of the tool.
It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.